Produced food travels from processing plants to grocery stores, where the food product remains on display case shelves for extended periods of time. For improved food quality, the food product should not exceed critical temperature limits while being displayed in the grocery store display cases. For uncooked food products, the product temperature should not exceed 41° F. For cooked food products, the product temperature should not be less than 140° F. In other words, the critical temperature limits are approximately 41° and 140° F. Between these critical temperature limits, bacteria grow at a faster rate.
One attempt to maintain food product temperature within safe limits is to monitor the discharge air temperature to ensure that the display case does not become too warm or too cold. But the food product temperature and discharge air temperature do not necessarily correlate; that is, discharge air temperature and food product temperature will not necessarily have the same temperature trend because food product temperatures can vary significantly from discharge air temperature due to the thermal mass of the food product. Further, during initial startup and display case defrost, the air temperature can be as high as 70° F. while food product temperature is much lower for this typically short interval. Finally, it is impractical to measure the temperature of food products at regular intervals in order to monitor food product temperature in a display case.
More specifically, in a conventional refrigeration system, a main controller typically logs or controls temperature. Conventionally, the main controller is installed in the compressor room, which is located on the roof or back of the grocery store. The conventional method for monitoring and controlling the display case temperature requires a discharge air temperature sensor mounted in the display case. The discharge air temperature sensor is typically connected to an analog input board, which is also typically located in the compressor room. A temperature wire must be pulled from the display case to the compressor room, which is typically difficult and increasingly expensive depending on how far away the compressor room is from the display case. Further, this wiring and installation process is more expensive and extremely cumbersome when retrofitting a store.